Field of the Invention
The present invention relates to a display device that allows for an auto-probe test and a method of testing the same.
Discussion of the Related Art
Various flat panel displays are being developed, including liquid crystal display devices (LCDs), organic light emitting diode displays (OLED displays), plasma display panels (PDPs), electrophoretic display devices (EPDs), etc.
A liquid crystal display displays an image by controlling an electric field applied to liquid crystal molecules in phase with a data voltage. In an active-matrix liquid crystal display, each pixel has a thin film transistor (hereinafter, referred to as “TFT”).
A manufacturing process of a liquid crystal display comprises a substrate cleaning process, a substrate patterning process, an alignment layer forming/rubbing process, a substrate bonding and liquid crystal dropping process, a drive circuit mounting process, a test process, a repair process, a liquid crystal module assembly process, etc.
In the substrate cleaning process, impurities on the surfaces of upper and lower glass substrates are removed with a cleaning solution. In the substrate patterning process, signal wires comprising data lines and gate lines, TFTs, pixel electrodes, a common electrode, etc. are formed on the lower glass substrate. Then, in the substrate patterning process, a black matrix, color filters, etc. are formed on the upper glass substrate. In the alignment layer forming/rubbing process, alignment layers are applied onto the glass substrates, and the alignment layers are rubbed with a rubbing cloth or optically aligned. Through these processes, data lines supplied with a video data voltage, gate lines intersecting the data lines and sequentially supplied with a scan signal, i.e., gate pulse, and a TFT array comprising TFTs formed at the intersections of the data lines and gate lines, pixel electrodes connected to the TFTs, and storage capacitors are formed on the lower glass substrate. In case of vertical electric field displays such as TN (Twisted Nematic) displays and VA (Vertical Alignment) displays, a common electrode is formed on the upper glass substrate. In case of horizontal electric field displays such as in-plane switching (IPS) displays and fringe field switching (FFS) displays, the common electrode, together with the pixel electrodes, is formed on the lower glass substrate. Polarizers are bonded to the upper and lower glass substrates, respectively.
In the substrate bonding and liquid crystal dropping process, a sealant is drawn to drop liquid crystals onto any one of the upper and lower substrates of the display panel, and the upper and lower glass substrates are bonded together with the sealant. A liquid crystal layer is defined by a liquid crystal area defined by the sealant.
In the drive circuit mounting process, an integrated circuit (IC) with a data drive circuit is bonded with an anisotropic conductive film (ACF) to data pads of the display panel by a chip-on-glass (COG) process or tape automated bonding (TAB) process. A gate drive circuit may be formed directly on the lower glass substrate by a gate-in-panel (GIP) process, or bonded with an ACF to gate pads of the display pane by the tape automated bonding (TAB) process during the drive circuit mounting process. In the drive circuit mounting process, ICs and a printed circuit board (PCB) are connected by a flexible circuit board such as a flexible printed circuit board (FPC), a flexible flat cable (FFC), etc.
The test process comprises a test on drive circuits, a wiring test on data and gate lines formed on a TFT array substrate, a test to be performed after the formation of pixel electrodes, electrical and lighting tests to be performed after the substrate bonding and liquid crystal dropping process, etc. In the repair process, any defects found in the test process are repaired.
Once the display panel is completed through the above-described processes, the liquid crystal module assembly process is conducted. In the liquid crystal module assembly process, a backlight unit is aligned under the display panel, and the display panel and the backlight unit are assembled using case tools such as a guide, casing member, etc.
The auto-probe test makes it possible to detect defects in the signal wires or thin film pattern on the substrates by conducting a lighting test on the substrates of the display panel prior to the drive circuit mounting process.
To enable the auto-probe test, auto-probe test pads (hereinafter, referred to as “AP pads”) coming into contact with needles of an auto-probe testing device are contacted to the lower glass substrate, and the wires (hereinafter, referred to as “AP wires”) connecting to the AP pads are connected to switching elements connected to the bottom of the display panel along the left and right bezels of the display panel. The AP pads AP are formed in a bezel area BZ outside an active area A/A, as shown in FIG. 1. However, the AP pads AP make it difficult for the display device to have a narrow bezel design. “PAD” of FIG. 1 denotes data pads connected to the ends of the data lines. Output signals from the ICs are fed to the data lines via the data pads. A pixel array for displaying an image is formed in the active area A/A. The bezel area is a non-display section outside the active area on the display panel.
The switching elements connected to the AP wires are individually connected to the data lines. Since the display panel has many switching elements subjected to a lighting test, the switching elements may increase the rate of defects in the display panel in the manufacturing process.
Because of the arrangement of the AP pads and the AP wires, the conventional auto-probe testing method does not allow for checking whether output terminals in the ICs and data links in the active area A/A are disconnected (or open). The data links interconnect the data pads and the data lines.
In wearable devices, display panels come in various designs. For example, display panels for smart watches are designed in a disc shape, and displays panels for automotive dashboards are designed in various curved shapes. Since these display panels have no space for the AP pads, the lighting test is not available.